Coke drum bottom throttling valve and system

ABSTRACT

A coke drum bottom de-heading system having an internal shroud enclosure and a shroud end cap opened by a flange to a coke bottom de-heading valve capable of accepting the end of a gate valve upon actuation. Acting in coordination with the shroud enclosure to prevent the escape of steam is a gate seal assembly having a gate seal slidably engaged against the sliding gate to prevent the passage of steam thereby.

RELATED APPLICATIONS

This application is a divisional application claiming priority to U.S.application Ser. No. 10/274,280 filed Oct. 18, 2002, and entitled, “COKEDRUM BOTTOM THROTTLING VALVE AND SYSTEM,” which claims priority toprovisional patent application Ser. No. 60/408,537, filed Sep. 5, 2002.

BACKGROUND

1. Field of the Invention

The present invention relates to a device and system for use with ade-heading vessel containing a fluid, distillates, or an unconsolidateddebris byproduct, such as the several types of coke. Specifically, thepresent invention relates to a system and device, namely a shroud foruse with a de-header valve and that is coupled to a coke drum whichserves to safely and effectively de-head the coke drum following theformation of coke, or other byproducts, to facilitate the removal ofcoke during the coking process.

2. Background

In the hydrocarbon processing industry, many refineries recover valuableproducts from the heavy residual oil that remains after refiningoperations are completed. This recovery process is known as delayedcoking and produces valuable distillates and coke in large vessels orcoke drums. Coke drums are usually in operation in pairs so that whenone coke drum is being filled with the byproduct or residual material,the feed may be directed to an empty drum so that the filled drum may becooled and the byproduct purged from the coke drum, a process known asdecoking. This allows the refinery process to operate in a continuousmanner, without undue interruption.

When one coke drum is full, it must be purged of the byproduct fed intoit. The drum is steam purged and cooled with quench water. The drum isthen drained of water and vented to atmospheric pressure, after whichthe top and bottom heads are removed (i.e. the coke drum is de-headed)to allow the coke to be cut from the drum and fall into a catch basin,typically a rail car. This process of de-heading the coke drum can beextremely dangerous for several reasons. To mention only a few, thecooling water introduced into the hot drums prior to the removal of thebottom head becomes extremely hot and could leak from the loosened headand scald surrounding operators, the load of un-drained water and loosecoke within the drum may exceed the limits of the support system andcause it to fail. Positioning the chute and necessary removal of theflanges or heads is done with operators who are in close proximity tothe drums, potentially falling coke may injure workers as the heads areremoved, and operating personnel may be exposed to finely divided cokeparticles, steam, hot water and noxious gases, when the drum is opened.Indeed several fatalities occur each year as a result of thismanufacturing process. Once the coke is removed, the heads are replacedand the coke drum is prepared to repeat the cycle.

Prior art systems and methods have tried too more efficiently andeffectively de-head coke drums, as well as to minimize many of thedangers inherent in the de-heading process. One such method involvesplacing a de-heading cart under the drum, raising a flange support ram,with braces installed, and loosening some (up to one half) of the flangebolts by manual operation with an impact wrench. Following the waterquench and drain, the remaining bolts are manually removed, braces areremoved from the ram, the approximately 4-ton flange is lowered, and thecart, with flange resting thereon, is moved away. This is extremelydangerous due to the manual labor requirements.

Other systems have been disclosed, which somewhat reduce human or manualinvolvement. For example, U.S. Pat. Nos. 4,726,109 to Malsbury et al.and 4,960,358 to DiGiacomo et al. describe a remote unheading device forcoking drums. The device includes a head unit for attachment to a lowerflange of a coking drum and a plurality of swing bolts which aredisconnected by remotely operated de-tensioning equipment. A platformdevice lowers the head unit, moves it laterally to one side and tips itfor cleaning. A chute attached to the frame can be raised intoengagement with the coking drum lower flange for removal of coke fromthe drum.

U.S. Pat. No. 5,098,524 to Antalfy et al. filed on Dec. 10, 1990discloses a coke drum unheading device having a pivoting actuator systemoperable from a location remote from a drum outlet. The actuator isadapted to move a drum head between closed and open positions and toretain the drum head in a closed position under a load.

U.S. Pat. No. 5,500,094 to Fruchtbaum provides a coke drum unheadingdevice that retracts and tilts the bottom head incrementally so thatfalling debris such as shot coke can be caught by a chute. Followingdisposal of the loose debris, the head can be withdrawn from the area ofthe drum for maintenance. Specifically, the invention provides anunheading device for removing a bottom head from a flange on a lower endof a coke drum. An unheading car is horizontally movable into and fromposition below the bottom head. A vertically adjustable bottom headsupport member is mounted on the car. A bearing plate is pivotallymounted at an upper end of the support member for engaging a lowersurface of the bottom head. A retractable arm has first and secondsections hingedly connected at one end and having respective oppositeends secured to the bearing plate and the support member for pivotingthe bearing plate and bottom head supported thereon with respect tohorizontal, preferably to tilt the head towards an adjacent chute.

U.S. Pat. No. 5,581,864 to Rabet discloses an apparatus and methodenabling removal of the drum head of a coke drum, which comprises anapparatus remotely placing a carriage under the drum head and thecarriage is adapted to remotely engage the drum head, tightly supportthe head against the drum while workers are in the area, and to lowerthe head and carry it away. A safety feature is also included anddisclosed, wherein the carriage is normally supported by springs which,in the event of excessive loads, automatically transfers the loadcarrier to an overhead beam designed to carry any excessive loads.

Each of these prior art devices share common deficiencies in that theyare incapable of providing simple, efficient, and safe solutions to thede-heading of a coke drum. Specifically, each of the assemblies ordevices require that the head unit be completely removed from the flangeportion of the coke drum after each coking cycle and prior to thepurging of the coke from the coke drum. This creates an extreme hazardto workers and provides an inefficient and time consuming procedure.Removal of the head unit increases the chance for accident, while at thesame time increases human involvement as the head unit must be properlyplaced on the coke drum each time despite the automation involved. Inaddition, a large amount of floor space is required to accommodate thoseassemblies and devices that automate the removal and lifting of the headunit from the coke drum. Finally, such devices and systems may not beoperable in an environment where there the bottom headroom is less thanthe diameter of the bottom head.

SUMMARY

A typical de-header system comprises a dual seated, linear motion goggleblind gate valve, or de-header valve, that is removably coupled to andseals against the flanged portion of a coke drum much the same way aconventional head unit would be attached. The de-header valve isequipped with a sliding blind having an orifice therein, a flat surfaceadjacent the orifice, a stroke slightly greater than the diameter of theorifice in the de-header valve, and upper and lower seats, wherein oneof such seats is a dynamic, live loaded seat that is capable ofautomatic adjustment so as to seal the blind between the upper seat. Assuch, the sliding blind can be moved in a substantially linearbi-directional manner between upper and lower seats, or dual seats, thuscausing the orifice located thereon to move between an open, closed, andpartially open position relative to the orifice in the coke drum. In aclosed position, the de-header valve and coke drum are prepared toreceive the byproduct feed from the refinery process used to manufacturecoke. Once the drum is full, the valve may be actuated causing thesliding blind to open. In doing so, coke that has accumulated on theblind is sheared by the upper and lower seats, thus de-heading the cokedrum and facilitating the removal of coke using methods commonly knownin the art.

The present invention operates in an environment wherein a coke drumde-heading system may comprise (a) at least one coke drum containingmanufactured coke therein, wherein the coke drum has a top orifice and abottom orifice; (b) a de-header valve removably coupled to the coke drumand designed to facilitate the removal of coke from the coke drum byde-heading the coke drum and allowing the coke to pass there through;and (c) an exchange system, including an upper and lower bonnet andother elements and members adapted to integrate the de-heading system,and particularly the de-header valve, into the manufacturing system. Thede-header valve itself may comprise (1) a main body having an orificedimensioned to align, in a concentric relationship, with either the topor bottom orifice of the coke drum when the de-header valve is coupledthereto; (2) a live loaded seat assembly coupled to the main body andcomprising a floating dynamic, live loaded seat, a live seat adjustmentmechanism coupled to the main body and designed to control and adjustthe force and resulting seat load of the dynamic, live loaded seat, anda force transfer module in juxtaposition to the dynamic, live loadedseat for transferring the force from the live loaded seat adjustmentmechanism to the dynamic, live loaded seat; (3) a static seat positionedopposite from and counteracting or counterbalancing the dynamic, liveloaded seat; and (4) a blind or sliding blind capable moving in alinear, bi-directional manner within the de-header valve and between thedynamic, live loaded seat and the static seat, the blind physicallycontrolled by an actuator and having a force exerted thereon by the dualseats, namely the dynamic, live loaded seat and the static seat, suchthat a seal is created between the dynamic, live loaded seat, the blind,and the static seat. In essence, the de-header valve de-heads the cokedrum and facilitates the removal of the coke from the coke drum uponactuation of the blind from a closed to an open position.

As the blind is actuated from a closed position, opening of the blindexposes the drum to the outside atmosphere. As can be seen in FIGS. 1Aand 1B, this causes depressurization of any residual pressure in thedrum and allows coke and any liquid contained within the drum to falldown the material discharge chute. By varying the speed of the actuationof the valve, the flow of this material may be regulated or throttled soas to prevent surges of material from flowing down the chute andoverwhelming the coke receiving area or any equipment below. In additionto the residual pressure in the drum, steam can also be released aroundthe blind if not properly prevented. For example, in order to preventoutflow of material from the drum, the valve is body pressurized with a20-PSI gradient above the pressure within in the drum. Upon actuation ofthe blind, there remains a 20-PSI steam pressure within the valve body.

The inventive shroud and side valve seals significantly reduce theamount of steam released through the open blind when the valve isthrottling. Upon complete closing of the blind, the shroud cap end plateis engaged overcoming a biasing pressure on shroud cap return springsand releasing steam pressure from the valve body into the shroud. Uponstroking of the valve in the opposite direction to open the the blind,the shroud cap return springs bias the cap closed on the end of theshroud to prevent any further migration of steam pressure from the bodycavity into the shroud. The benefits of the shrouding closure and valveside gate seals is that the amount of steam lost from the system duringthe throttling is greatly reduced and the shroud prevents dropping ofany coke which accompanies the movement of the opening of the blindvalve from falling into the bonnet. This is especially important in athrottling situation where the inner diameter of the opening of theblind will communicate with the interior of the shroud for extendedperiods of time thus having a greater opportunity to retain cokefragments. The openings in the gate valve also have an opportunity tofill. Without the shroud, this material would be deposited in the bonnetupon actuation of the valve. Instead, because of the close tolerancebetween the shroud and the blind, any deposited materials will accompanythe blind as it is actuated and be pushed out through the downstreamport of the valve as the valve is closed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cutaway view of the entire valve body demonstrating theinteraction between the blind orifice and the valve body in the closedposition (bonnets removed for clarity);

FIG. 2 is a perspective view of the valve body and shroud;

FIG. 3 is a an exploded view of the gate seal assembly;

FIG. 4 is a cross-sectional view taken through the gate seal of FIGS. 2and 3 demonstrating the interaction between the internal components; and

FIG. 5 is a cross-sectional view of a nose ring inside a blind.

DETAILED DESCRIPTION OF THE PREFERRED EMDODIMENTS

It will be readily understood that the components of the presentinvention, as generally described and illustrated in the figures herein,could be arranged and designed in a wide variety of differentconfigurations. Thus, the following more detailed description of theembodiments of the system, device, and method of the present invention,as represented in FIGS. 1A-4, is not intended to limit the scope of theinvention, as claimed, but is merely representative of the presentlypreferred embodiments of the invention.

The presently preferred embodiments of the invention will be bestunderstood by reference to the drawings wherein like parts aredesignated by like numerals throughout. Although reference to thedrawings and a corresponding discussion follow below, it is firstadvantageous to provide a general background of the coking process,including the process of de-heading the coke drums at the end of amanufacturing cycle.

General Discussion on Delayed Coking and Coke De-Heading

In the typical delayed coking process, high boiling petroleum residuesare fed to one or more coke drums where they are thermally cracked intolight products and a solid residue - petroleum coke. The coke drums aretypically large cylindrical vessels having a top head and a conicalbottom portion fitted with a bottom head. The fundamental goal of cokingis the thermal cracking of very high boiling point petroleum residuesinto lighter fuel fractions. Coke is a byproduct of the process. Delayedcoking is an endothermic reaction with a furnace supplying the necessaryheat to complete the coking reaction in a drum. The exact mechanism isvery complex, and out of all the reactions that occur, only threedistinct steps have been isolated: 1) partial vaporization and mildcoking of the feed as it passes through the furnace; 2) cracking of thevapor as it passes through the coke drum; and 3) cracking andpolymerization of the heavy liquid trapped in the drum until it isconverted to vapor and coke. The process is extremelytemperature-sensitive with the varying temperatures producing varyingtypes of coke. For example, if the temperature is too low, the cokingreaction does not proceed far enough and pitch or soft coke formationoccurs. If the temperature is too high, the coke formed generally isvery hard and difficult to remove from the drum with hydraulic decokingequipment. Higher temperatures also increase the risk of coking in thefurnace tubes or the transfer line. As stated, delayed coking is athermal cracking process used in petroleum refineries to upgrade andconvert petroleum residuum (or resid) into liquid and gas productstreams leaving behind a solid concentrated carbon material, or coke. Afired heater is used in the process to reach thermal crackingtemperatures, which range upwards of 1,000° F. With short residence timein the furnace, coking of the feed material is thereby “delayed” untilit reaches large coking drums downstream of the heater. In normaloperations, there are two coke drums so that when one is being filled,the other may be purged of the manufactured coke. These coke drums arelarge structures that are approximately 25-30 meters in height and from4 to 9 meters in diameter. They are equipped with a top blind flangeclosure or orifice that is typically about 1.5 meters in diameter, and abottom blind flange orifice that is typically about 2 meters indiameter.

In a typical petroleum refinery process, several different physicalstructures of petroleum coke may be produced. These are namely, shotcoke, sponge coke, and/or needle coke, and are each distinguished bytheir physical structures and chemical properties. These physicalstructures and chemical properties also serve to determine the end useof the material. Several uses are available for manufactured coke, someof which include fuel for burning, the ability to be calcined for use inthe aluminum, chemical, or steel industries, or the ability to begasified to produce steam, electricity, or gas feedstock for thepetrochemicals industry.

To produce the coke, a delayed coker feed originates from the crude oilsupplied to the refinery and travels through a series of process membersand finally empties into one of the coke drums used to manufacture coke.The delayed coking process is a batch-continuous process, which meansthat the process is ongoing or continuous as the feed stream coming fromthe furnace alternates filling between the two or more coke drums. Asmentioned, while one drum is on-line filling up with coke, the other isbeing stripped, cooled, decoked, and prepared to receive another batch.This is a timely process, with each batch in the batch-continuousprocess taking approximately 12-20 hours to complete. In essence, hotoil, or residue as it is commonly known, from the tube furnace is fedinto one of the coke drums in the system. The oil is extremely hot (95°F.) and produces hot vapors that condense on the colder walls of thecoke drum. As the drum is being filled, a large amount of liquid runsdown the sides of the drum into a boiling turbulent pool at the bottom.As this process continues, the hot residue and the condensing vaporscause the coke drum walls to heat. This naturally in turn, causes theresidue to produce less and less of the condensing vapors, whichultimately causes the liquid at the bottom of the coke drum to start toheat up to coking temperatures. After some time, a main channel isformed in the coke drum, and as time goes on, the liquid above theaccumulated coke decreases and the liquid turns to a more viscous typetar. This tar keeps trying to run back down the main channel which cancoke at the top, thus causing the channel to branch. This processprogresses up through the coke drum until the drum is full, wherein theliquid pools slowly turn to solid coke. When the first coke drum isfull, the hot oil feed is switched to the second coke drum, and thefirst coke drum is isolated, steamed to remove residual hydrocarbons,cooled by filling with water, opened, and then decoked. This cyclicalprocess is repeated over and over again in the manufacture of coke.

The decoking process is the process used to remove the coke from thedrum upon completion of the coking process. Due to the shape of the cokedrum, coke accumulates in the area near and attaches to the heads duringthe manufacturing process. To decoke the drum, the heads must first beremoved. Typically, once full, the drum's contents are stripped andwater quenched down to a temperature of 200° F. or less and vented toatmospheric pressure and the top head (typically a 4-foot diameterflange) is unbolted and removed to enable placement of a hydraulic cokecutting apparatus. After the cooling water is drained from the vessel,the bottom head (typically a 6-foot-diameter blind plate quench) isunbolted and removed. This process is commonly known as “de-heading” andcan be a very dangerous procedure because of the size of the heads, thehigh temperatures within the drum, potential falling coke, and otherreasons as mentioned above. Once the heads are removed, the coke isremoved from the drum by drilling a pilot hole from top to bottom of thecoke bed using high pressure water jets. Following this, the main bodyof coke left in the coke drum is cut into fragments which fall out thebottom and into a coke receiving area, and in some cases into, a bin ora rail cart, etc. The coke is then dewatered, crushed and sent to cokestorage or loading facilities.

Present Invention Coke Drum De-Heading System

Although the present invention is applicable and utilized on both thetop and bottom openings of a coke drum, the following detaileddescription and preferred embodiments will be discussed in reference toa bottom de-heading system only. One of ordinary skill in the art willrecognize that the invention as explained and described herein for acoke drum bottom de-heading system may also be designed and used as acoke drum top or side de-heading system and the following discussionpertaining to the bottom de-heading system is not meant to be limitingto such.

The present invention is used in conjunction with a device forde-heading a coke drum following the manufacture of coke therein. As thepresent invention is especially adapted to be used in the cokingprocess, the following discussion will relate specifically in thismanufacturing area. It is foreseeable however, that the presentinvention may be adapted to be an integral part of other manufacturingprocesses producing various elements other than coke, and such processesshould thus be considered within the scope of this application.

The present invention comprises a shroud and gate seal assembly. Theinventive shroud and gate seal assembly may be used in conjunction witha dual seated, linear motion, goggle blind valve or other types ofde-heading gate valves. FIGS. 1A and 1B depict the environment in whicha typical de-heading gate valve is employed. As can be seen in moredetail in FIG. 2, a shroud 20 is shown attached to a valve body 22. Theshroud has a shroud cap 24, shroud body 26 and springs 28 which bias theshroud cap 24 against shroud body 26. Upon actuation of the valve, ablind is moved from an open position as shown in FIG. 2 and as the blindtravels from the open position, it contacts shroud end cap 24 andreleases steam pressure built up within shroud body 26. Upon actuationof the blind in the opening direction, the blind will move away fromcontact with shroud cap 24 allowing spring 28 to bias cap 24 againstshroud body 26 thereby sealing the shroud and preventing the escape ofsteam. Shroud 20 is attached to valve body 22 by a flange 30. It isimportant that the shroud be aligned with the valve body 22 to allowproper passage of the blind as it is actuated. The tolerances andclearances between the blind and the shroud body are important. Anyresidual coke that follows the blind into the shroud must either remainwithin the blind or must be held within the shroud so that it does notfall into the lower bonnet of the valve. Any coke particulate heldwithin the shroud will be acted upon by the steam and much of it will beejected from the shroud cap as it is encountered by the end of the blindas it is actuated.

Turning now to another portion of the inventive system, a gate sealassembly 32 is shown located within valve body 22 in FIG. 2. FIG. 3depicts an exploded view of the contents of the assembly which comprisesa seal cap 34, a guide cup 36, a load spring 38, and seal plate 40, anda gate seal 42. Seal cap 40 is used to hold the contents inside valvebody 22. Guide cups 36 serves to guide the movement of gate seal 42which floats freely therein and operates against the sides of the blind.Because the seal between gate seal 42 and the side of the blind is notperfect, load spring 48 provides pressure against guide seal 42 toinsure a fit which will prevent the flow, or at least reduce the flow ofsteam there through. Since valve body 22 has internal components whichare under a constant positive pressure to prevent the flow ofcontaminates from the drum into the valve body, actuation of the blindallows pressure to flow out of the pressurized body cavity through theup stream and downstream ports of the valve. This pressure loss canresult in a negative pressure boundary flowing from the drum into thebody cavity. Gate seal 42 prevents the escape of this steam or at leastreduces it to the point where the escape is minimal. Thus the bodycavity retains a positive pressure over that of the drum.

Turning now to FIG. 4, a cross-sectional view taken along lines AA andFIG. 2 is depicted. The interaction between gate seal 22 and gate 44 isdepicted. Gate seal assembly 32 remains statically in place as gate 44moves in a linear manner when actuating the valve. The interface betweenthe two components is kept tight by the pressure from load spring 38against gate seal 32. Gate seal 32 is comprised of a material such as ametal impregnated graphite composite which maintains a tight seal andalso provides some limited degree of lubrication to allow gate 44 toslide thereby. Seal cap 34 allows access to these internal componentsfor maintenance and replacement.

FIG. 5 is a cross-sectional view of a nose ring 60 inside the orifice 62of a blind 64. When used for throttling, the area around the orificeedge is exposed to harsh conditions including heat, friction andpressure. To increase the life of the blind, a replaceable nose ring 60is installed. Nose ring 60 must have extremely close tolerances toremain attached to blind 64. Downward pressure on the inner edge willurge the ring out of the blind. To resist the pressure from coketraveling over the ring, a ring bolt or retainer extends from the lowerface of the blind to secure the ring in place. The ring should beconstructed of a strong material such as grade 5 12 chrome nitrided 4/10stainless steel or other wear resistant material.

1. A system for preventing the escape of an undue amount of steam from acoke de-heading device as it is being throttled, said system comprising:a shroud enclosure capable of completely surrounding a linear blind gatevalve as the blind is actuated thereby containing any released steam orcoke debris and preventing that debris from being deposited into thevalve bonnet; and a blind seal assembly having a blind seal slidablyengaged against the blind to prevent the flow of steam thereby.
 2. Asystem as recited in claim 1, wherein the blind is configured toselectively slide between an opened position and a closed position.
 3. Asystem as recited in claim 4, wherein when the blind is in the closedposition, a shroud cap end plate of the shroud overcomes a biasingpressure from one or more shroud cap return springs and releases steampressure from a valve body into the shroud.
 4. A system as recited inclaim 5, wherein when the blind is in the opened position, the one ormore shroud cap return springs bias the shroud cap end plate to preventa release of the steam pressure from the valve body into the shroud. 5.A system as recited in claim 1, wherein the system is one of: (i) abottom de-heading system; (ii) a top de-heading system; and (iii) a sidede-heading system.
 6. A system as recited in claim 1, further comprisinga gate seal assembly coupled to a body of the blind gate valve, whereinthe gate seal assembly is configured to float within a guide cup toreduce an amount of steam from escaping from the body when pressurized.